We are running the Flat File to XML adapter in an ESB process. We have set up multiple instances of the adapter in an attempt to do conversions in a multi-thread manner however the adapter still seems to only be parsing one record at a time. Is there a way to multi-thread the adapter?

Nothing in the adapters themselves is single-threaded - they were
designed to be thread-safe.

But you've given us almost no useful information for us to help
you - not even which ESB you are using, nor the release of the
adapters. Also, what is your machine architecture? And how have
you determined that you are only getting one row at a time?